Research On The Degradation Mechanism And Improvement Of The Storage Performance Based On LiCoO₂ Lithium-ion Battery

With the increase of energy consumption and the environments protection consciousness of people,lithium-ion battery has become an essential part of our life.However storage can not be avoided during use,the storage performance of lithium-ion battery is a very important performance indicators and even becomes one of the key factors restricting its use.At present,the researches on the degradation mechanism of storage performance and how to improve storage performance are less.So this paper mainly studies the storage performance and degradation mechanism of LiCoO₂lithium-ion battery.Also the life analytic and predicting model is established.Last we try to improve the storage performance of the battery by the additions of electrolyte additives.First,this paper studies the storage performance of LiCoO₂ lithium-ion battery at different temperature,and we explore the degradation mechanism of the storage performance by means of EIS and XPS.Based on the experiment data and mechanism analysis,the life analytic and predicting model is established.Studies have shown that both the positive and negative active materials are exposed in the electrolyte because of the incompleteness of surface film.During storage,the electrochemical oxidation-reduction side reactions of the solvent components can take place on the surface of electrodes.The lithium salt will decompose at the same time.During storage,the capacity retention and rate performance become degrade.Meanwhile internal resistance is increased.The higher the temperature,more serious the performance becomes.Finally,based on the mechanism analysis,we have established the relationship of storage capacity loss,storage time and temperature:???.This model can reflect the relationship of storage capacity loss,storage time and temperature under certain condition much better.The completeness of film and stability of lithium salts are key factors that affect the storage performance of lithium-ion battery.First we study the impact of film-forming additive LiBOB on the storage performance of lithium-ion battery.Studies show that LiBOB can promote the positive electrode forming a more stable surface film.Meanwhile the surface of the negative electrode is formed of a series of stabile oxalate borate oligomer and Li2CO3,which can enhance storage performance of battery.Compared with the battery that doesn't contain LiBOB,the capacity retention and rate capability of battery which contain LiBOB are improved.Internal resistance is decreased.When the ratio is 3%,the storage performance becomes best.Finally,we study the impact of lithium salt stabilizer DMAC on the storageperformance of lithium-ion battery.Studies have shown that the DMAC additive-containing electrolyte has a good compatibility with graphite anode and LiCoO₂ positive electrode.But it can't promote the formation of Li2CO3.On the contrary it will destroy the surface film of the positive electrode.This will cause decomposition of the active material and dissolution of cobalt in the positive electrode.Also it accelerates the oxidation rate of electrolyte on the surface of the anode during storage.So the storage performance becomes deteriorate.Compared with the battery that doesn't contain DMAC,the capacity retention and rate capability of battery which contains DMAC become more serious.Internal resistance increases more obviously.The greater the proportion,the worse the storage performance becomes.